1. Field of Invention
This invention relates to invasive medical devices. In particular, this invention relates to a locking dilator associated with a peel away introducer sheath used for the introduction of catheters and other such medical devices into a patient.
2. Prior Art
For many medical purposes it is important to introduce devices through the skin and underlying tissue layers into blood vessels or other locations inside the body of a patient. These purposes include, but are not limited to the introduction of catheters, pacemaker leads and other such devices into a patient's body. These devices are transcutaneous devices which pass through the skin and into the blood vessel during use.
Several methods have been designed to place such devices within the body. Perhaps the earliest method was to cut an opening in the body, insert the device and then close the wound around the device. One example of this method is known as the "cut-down" placement method. Disadvantages are associated with this method because of the high skill necessary for its precise use as well as the specialized medical facilities necessary to perform the procedure safely. Further, because of differences in medical personnel and in patients, trauma, disruptions and infection risks increase to the tissues involved where this method is employed.
To alleviate some of these disadvantages, percutaneous methods have been developed to create small openings in the tissue and then to employ various devices to slightly enlarge the opening to permit the insertion of specialized medical instruments. One such device commonly used is a dilator. The dilator has a tapered end which will enlarge the opening at the puncture site as the dilator is advanced through the tissue. Once the tissue is enlarged, the dilator is removed and the desired catheter or other medical device is quickly inserted through the opening created. This method is subject to many problems because of trauma, bleeding of the patient and the difficulty of insertion of certain specialized medical instruments in such an opening. Besides the possibility of reclosing of the opening prior to insertion of the secondary medical instrument, many types of medical devices, including pacemaker leads are extremely soft and supple or will damage the body during insertion if not surrounded by some introducing means.
Further, it is important to keep the size of these invasive devices as small as possible to create the smallest opening within the body. However, many of the devices introduced have sections which are quite large, principally on a portion of the device located outside of the inserted portion. To pass such a device through an introducer sheath, the introducer sheath must be made with an internal passageway at least as large as the largest part of the device so that the introducer sheath may be removed following device placement in the body. Further, if such enlarged opening is created in the body, when the thin part of the device is advanced, there will now be much empty space creating a pathway for body fluids to pass around the device and escape from the body increasing the risk of clotting, infection, etc.
A device which solves this problem is the peel away introducer sheath used in conjunction with a dilator. The peel away introducer sheath is a thin-walled, usually cylindrical, device that is placed in position so that it provides a communicating passageway through the tissue. This is often accomplished by fitting the introducer sheath tightly over a dilator, advancing both devices through the tissue together as a unit, and then removing the dilator from inside the introducer sheath, leaving the introducer sheath alone in the desired position, acting to hold the penetrated site open. At that point, the catheter tube or other invasive device is advanced through the introducer sheath into the desired position The peel away introducer sheath is then removed from the tissue and pulled apart lengthwise into two pieces. This capacity for splitting allows the introducer sheath to be made as small as the inner compartmental portion of the inserted medical device. The introducer sheath is then pulled apart and removed. Proximal handles on the introducer sheath are generally provided to facilitate grasping of the introducer sheath halves.
Several types of peel away introducer sheaths are known in the prior art. For example, U.S. Pat. No. 4,983,168 discloses a layered peel away hollow sheath wherein the sheath wall is comprised of at least two layers, the inside layer being cylindrical and the outside layer comprising two semi-cylindrical segments defining opposed axially-directed slits or slots there between which comprise tear lines such that the sheath manually tears axially along the single layered tear line into two pieces for removal of the sheath from around the indwelling device.
U.S. Pat. No. 4,596,559 discloses a tear away introducer tool for use with a disposable introducer set in conjunction with a catheter. The tear away introducer is comprised of an elongated sheath having a pair of opposed splits in the proximal end which define a pair of tabs. A handle is secured to the sheath and includes a pair of handle members, each comprising a pair of clamping elements which clamp the tabs of the sheath there between. The handle has opposed weakened portions which facilitate the tearing of the sheath along axial lines.
U.S. Pat. No. RE 31,855 discloses a sheath that has an internal molecular orientation which tears easily in a lengthwise direction and with great difficulty in a cross-wise or oblique directions. See also U.S. Pat. No. 4,581,025.
U.S Pat. Nos. 4,166,469, 4,243,050, 4,345,606 and 4,451,256 disclose sheaths longitudinally scored or perforated on opposite sides. This results in a cylindrical sheath with two weakened lines which run lengthwise on opposite sides of the cylinder. The introducer or sheath is thus mechanically weakened along its scored or perforated regions and less resistant to tearing than the rest of the sheath cylinder, causing the tear once started to propagate along the weakened region. See also U.S. Pat. No. 4,451,256.
Regardless of which of these types of peel away introducer sheaths is used, there is a tendency for the dilator to rearwardly migrate into the introducer sheath when the medical practitioner attempts to forcibly enlarge the introduction site by driving the tapered leading edge of the tip of the dilator through the skin and subcutaneous tissue. This tendency makes manipulation not only difficult but also traumatic for the patient. Further, the introducer sheath may be damaged, requiring use of a new invasive device.
One method of addressing this problem is disclosed in U.S. Pat. No. 4,772,266. Incorporated in the proximal end of the dilator is a female coupling element, the interior of which comprises a helically directed luer loc mechanism. The proximal end of the introducer sheath contains a male luer loc coupling member which works in combination with the female coupling member of the dilator. As the female coupling member is axially rotated around the male coupling member of the introducer sheath, the dilator and the introducer sheath are releasably locked in position. This device is cumbersome to the medical practitioner considering that the practitioner is gloved and manipulation of the device is difficult.
Another method of preventing the undesired migration of the dilator within the introducer sheath is disclosed in U.S. Pat. Nos. 4,243,050 and 4,345,606. In these patents the proximal end of the dilator contains a hub with a lip. The proximal end of the introducer sheath contains a flange, a portion of which fits between the hub and the flange under appropriate circumstances to prevent undesired migration of the dilator within the introducer sheath.
Although not used with a dilator and introducer sheath, U.S. Pat. No. 4,362,156 discloses an intravenous infusion assembly wherein a catheter assembly and a needle assembly are releasably locked together at their proximal ends to prevent relative axial movement there between during insertion into the vein. Clamp arms are an element of the needle assembly wherein said clamp arms contain hooks which engage the lugs on the catheter assembly. Operating in conjunction with the clamp arm and hook are an interfitting tenon on the needle assembly and a notch on the catheter assembly. The combination of all of these elements when interlocked are required to limit relative rotation between the needle assembly and the catheter assembly.
Another method of preventing the migration of the dilator within the introducer sheath is an interlocking mechanism manufactured by Angeion as disclosed in Journal of Invasive Cardiology, Vol. 1, No. 5, p. 249 (1991) and Angeion advertising material of 1991. This mechanism is a one piece device containing an arm which fits below the handle of the introducer sheath and a slotted portion which is secured on the proximal end of the dilator. These two elements working together restrict the dilator from migrating inside the introducer sheath.
Many of the devices previously disclosed provide a method to limited undesirable rearward migration of the dilator into the introducer sheath during the introduction of the dilator within the patient. However, more reliable dilator/introducer sheath assemblies are necessary to prevent problems associated with this migration.
Therefore, it is an object of this invention to provide an improved dilator/introducer sheath set.
It is a further object of this invention to provide an improved dilator/introducer sheath for the unstressed introduction of catheters and other such medical devices into patients.
It is a still further object of the present invention to provide a novel dilator/introducer sheath device which creates a secure relationship between the dilator and introducer sheath to prevent the dilator from rearward migration into the introducer sheath.
These and other objects and features of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description, drawings and claims. The description, along with the accompanying drawings, provide a selected example of the construction of the device to illustrate the invention.